Patent GB-1284442-A (GB)
Title: Method and electro-optical system for inspecting bodies such as tiles
Inventor: WEST ROBERT NOEL
IPC: G01N21/89
Filed: 1969-01-17
Abstract: 1284442 Photo-electric investigation of defects SIRA INSTITUTE 19 Jan 1970 [17 Jan 1969] 2971/69 Heading G1A A body is inspected for various faults by passing it through a plurality of stations where it is subjected to electro-magnetic radiation, the body being turned through 90 degrees after passing a number of stations. The apparatus described is used for inspecting tiles for edge chips or lumps, (stations 10, 17), glaze flaws (stations 12, 19) and colour spots on or under the glaze (stations 14, 21) and includes devices for marking faulty tiles and ejecting them at station 22. As seen in Fig.1, the complete inspection of the tile requires two sets of stations with an intermediate tile turning station 16. The tile is carried on a split conveyor 31a, 31b so that photo-cells 39, 40 can be used to indicate when the leading and lagging edges of the tile pass. The side edges of the tile are illuminated by centrally disposed source 30, Fig. 2, with collimating lenses 33, 34 and the unobstructed light is detected by photo-cells 35, 36 whose outputs are subtracted to give a zero output over the period when elements 39, 40 are not illuminated thus indicating a perfect tile. The station 17 works in an identical manner on the other two edges of the tile. Glaze flaws: These are detected by investigating the specular reflection from the surface of the tile when illuminated by a long Q1 lamp m, Fig. 39. An optical scanning member 50 comprising a rotating drum 5 with lenses 51 arranged around its periphery is arranged to focus the reflected light on to a slit 110 where it is detected by a photo-cell (not shown). Lens 112, tilted to avoid specular reflections, and adjustable slit 113 provide the required resolution. A disc attached to member 50 is provided with an array of slots and an array of holes, which in co-operation with a photo-cell, produce gating pulses corresponding to the duration of time a lens takes to scan the tile surface, and clock pulses respectively. The clock pulses are used to count down the time from the edge of the tile so that edge effects do not cause a defect indication and this provides greatest sensitivity over the major width of the tile, Figs. 15, 20 (not shown). A glaze defect is identified when the differentiated output of the pulse obtained from each lens scan exceeds a given level. Colour spots on or under the glaze: These are detected using apparatus, Fig. 21, similar to that used to detect glaze flaws except that the light source is arranged so that the scanning detector receives only diffused reflected light. An elongated light source is used or mirrors employed to make the light source appear infinitely long. The arrangement detects both faults under the glaze and can be adapted to recognise colour changes extending across the tile. In a modification, Fig. 35 (not shown), the chip detector is modified to also check the edge glaze of the tile by reflecting light off the edges of the tile to detectors as well as detecting the light passing the edge. The backing and lagging edges can be checked for chips at the same time by scanning across the tile and checking the number of pulses gated in each scan. The presence of a chip or lump will be seen as a reduced or greater number. In a further modification the tile may be supported on a plater which provides the edge effects so that the full width of the tile is accurately checked.